The present invention relates to a method and apparatus for optimizing the operating characteristics of an engine. In particular, the invention relates to a method and apparatus for minimizing the specific fuel consumption of a reciprocating piston engine.
Engine control systems that detect and control various engine operating characteristics in a closed-loop are known. Such engine control systems may include a central processing unit, such as a microprocessor, whereby various engine sensors associated with the engine are read and various engine effectors are controlled in accordance with closed-loop control laws or equations. Such engine control systems may include the capability of optimizing various engine operating characteristics. However, such optimization techniques require that the optimum operating characteristics be predetermined. Such a system automatically controls various engine variables in accordance with predetermined control laws in an effort to obtain these predetermined optimum conditions.
A disadvantage of the above-described system is that the optimum operating conditions may vary depending upon the instantaneous operating characteristics of the engine. That is, the control laws for moving the engine effectors as a function of the control system inputs are unable to be effectively altered as a function of the various changes in the engine operating characteristics, thus resulting in inefficient and inaccurate optimization.
An optimum control method for an internal combustion engine is disclosed in U.S. Pat. No. 4,322,800. The patent discloses a method for controlling an engine such that the engine is operated at a minimum rate of fuel consumption. At least one engine control variable is arranged in the form of a map with respect to various engine operating conditions and this mapped engine control variable is changed to compensate for variation in the engine operating conditions. However, such system does not consider if the engine variables have limited operating ranges and thus does not consider if the variables are driven outside their ranges during minimization. Moreover, the changes made to the map are permanent.